Laravel - insert data into a table that contains id of other tables - sql

Question

i have a table in my database( table case ) that contains case type id which is a foreign key to the table (case_type). when users fill this table they dont know the case type id they only know the category of the case. so what i want to do is when users fill the case table they write the case type category and based on that it match the category with the case id since i have a separate table and submit that id in to the case table.
so far what i have tried :
from vue i send the category selected from a dropdown by the user to this controller function
public function getIdOfCategoryByName(Request $request){
$name = $request->input('name');
$getidbyname=case_type::where('category',$name)->get('id');
return $getidbyname;
}
this is where i dont know how to insert the id that i got back to this function
public function createcase(){
$request->validate([
'title' => 'required',
'description' => 'required',
'caseTypeId' => 'required',
'amountreceived' => 'required',
'amoutneeded' =>'required',
'uid' => 'required',
'visible' => 'required',
'image' => 'required',
'cityId' => 'required'
]);
waitingdonations::create($request->post());
return response()->json([
'message' => 'waiting donation successfull',
]);
}
if my question is unclear please check this website https://towardsdatascience.com/sql-insert-values-with-joined-ids-from-another-table-83ff7f149296